A social media strategy is a document that contains and lists out the plan of action a company intends to implement to reach its desired goal on social media.                                  

In simpler words, it is a document that displays all the essential steps a company has thought up and decided that implementing these steps on social media would take them to their long-term goal and overall aim. When you pen down a list of plans that guide your actions, defines your objectives, tactics, and end goals, then you have created a strategy.